Issue 2021-2 July 2021 FACS A C T S The Newsletter of the Formal Aspects of Computing Science (FACS) Specialist Group ISSN 0950-1231 FACS FACTS Issue 2021-2 July 2021 About FACS FACTS FACS FACTS (ISSN: 0950-1231) is the newsletter of the BCS Specialist Group on Formal Aspects of Computing Science (FACS). FACS FACTS is distributed in electronic form to all FACS members. Submissions to FACS FACTS are always welcome. Please visit the newsletter area of the BCS FACS website for further details at: https://www.bcs.org/membership/member-communities/facs-formal-aspects- of-computing-science-group/newsletters/ Back issues of FACS FACTS are available for download from: https://www.bcs.org/membership/member-communities/facs-formal-aspects- of-computing-science-group/newsletters/back-issues-of-facs-facts/ The FACS FACTS Team Newsletter Editors Tim Denvir [email protected] Brian Monahan [email protected] Editorial Team: Jonathan Bowen, John Cooke, Tim Denvir, Brian Monahan, Margaret West. Contributors to this issue: Jonathan Bowen, Andrew Johnstone, Keith Lines, Brian Monahan, John Tucker, Glynn Winskel BCS-FACS websites BCS: http://www.bcs-facs.org LinkedIn: https://www.linkedin.com/groups/2427579/ Facebook: http://www.facebook.com/pages/BCS-FACS/120243984688255 Wikipedia: http://en.wikipedia.org/wiki/BCS-FACS If you have any questions about BCS-FACS, please send these to Jonathan Bowen at [email protected]. 2 FACS FACTS Issue 2021-2 July 2021 Editorial Dear readers, Welcome to the 2021-2 issue of the FACS FACTS Newsletter. A theme for this issue is suggested by the thought that it is just over 50 years since the birth of Domain Theory1. Why did computer science need Domain Theory? To provide a semantics for computational structures, one needs to construct a mathematical model for them. In many high-level programming languages it is possible to define recursive data types, and to write successful programs which use them. Yet it is impossible to model recursive data types, such as those that contain their own function spaces, in set theory. Georg Cantor showed this in about 1874-18842. Where data types embody functions, they are computable functions, not the fully fledged functions found in set theory. Domains provide a way of expressing these limited functions, which has, almost happily, the accidental effect of enabling types to have this kind of recursion. Programming languages were not the first context in which we find recursion. Developments in mathematical logic, in the early 20th century, used the idea decades before. In their introduction to the second edition of Principia Mathematica3 Whitehead and Russell refer to that theorem of Cantor’s, stating it very succinctly: 2n > n Here 2 denotes the two-value set {0,1}, n denotes the set of natural numbers [0:n-1], 2n denotes the set of functions from n to 2 and > compares the cardinalities of the sets. Whitehead and Russell remark that Cantor’s proof is limited to finite sets n, but if that historically is the case, it is easy to extend a natural proof to infinite sets of any cardinality (left to the reader!). (Note that if n is countably infinite, then the theorem and proof are isomorphic to another strongly related theorem of Cantor’s, that the Reals are uncountable). Enough of this from me. Our first feature article is by my co-editor, Brian Monahan, Domain Theory Revisited, an introduction and thoughtful discourse on the subject. Then comes John Tucker, Haskell B. Curry at War, a historical note from the History of Computing Collection at Swansea University. The third feature is by Glynn Winskel, Domain Theory and Interaction. This is a splendid grand tour of the history from Domain Theory’s beginnings, through interactive computation, concurrent games and 1Dana S. Scott. Outline of a mathematical theory of computation. Technical Monograph PRG-2, Oxford University Computing Laboratory, Oxford, England, November 1970; Dana Scott and Christopher Strachey. Toward a mathematical semantics for computer languages Oxford Programming Research Group Technical Monograph. PRG-6. 1971. 2See e.g. https://mathshistory.st-andrews.ac.uk/Biographies/Cantor/ 3Alfred North Whitehead & Bertrand Russell, Principia Mathematica, CUP 1910, second edition 1927, paperback edition to *56 1962, page xiv. 3 FACS FACTS Issue 2021-2 July 2021 strategies, to recent work on dialectica categories and container types. Then, Andrew Johnstone provides a most instructive review of the recent book by Cliff Jones, Understanding Programming Languages (Springer Switzerland 2020), again extremely relevant to program language semantics. Finally we have reports on some recent FACS and FACS-related events. Keith Lines summarises the webinar by Conor McBride & Fredrik Nordvall Forsberg, Dimensionally correct by construction: Type systems for programs. Jonathan Bowen details the ABZ 2021 conference, which was preceded by a festschrift for Egon Börger. Jonathan also covers FACS and other relevant seminars that have taken place so far this year: Keith Lines, NPL’s Experience with Formal Aspects; Marta Kwiatkowska, Probabilistic Model Checking for the Data-rich World (BCS Lovelace seminar); and Michael Leuschel, New Ways of Using Formal Models in Industry (joint FACS and FME seminar). We hope you enjoy FACS FACTS issue 2021-2. Tim Denvir Brian Monahan 4 FACS FACTS Issue 2021-2 July 2021 5 FACS FACTS Issue 2021-2 July 2021 6 FACS FACTS Issue 2021-2 July 2021 7 FACS FACTS Issue 2021-2 July 2021 8 FACS FACTS Issue 2021-2 July 2021 9 FACS FACTS Issue 2021-2 July 2021 10 FACS FACTS Issue 2021-2 July 2021 11 FACS FACTS Issue 2021-2 July 2021 12 FACS FACTS Issue 2021-2 July 2021 13 FACS FACTS Issue 2021-2 July 2021 14 FACS FACTS Issue 2021-2 July 2021 15 FACS FACTS Issue 2021-2 July 2021 16 FACS FACTS Issue 2021-2 July 2021 17 FACS FACTS Issue 2021-2 July 2021 18 FACS FACTS Issue 2021-2 July 2021 19 FACS FACTS Issue 2021-2 July 2021 20 FACS FACTS Issue 2021-2 July 2021 21 FACS FACTS Issue 2021-2 July 2021 22 FACS FACTS Issue 2021-2 July 2021 23 FACS FACTS Issue 2021-2 July 2021 24 FACS FACTS Issue 2021-2 July 2021 25 FACS FACTS Issue 2021-2 July 2021 26 FACS FACTS Issue 2021-2 July 2021 References [1] Samson Abramsky, Domain theory in logical form, Annals of Pure and Applied Logic, 51:1–77, 1991 https://www.sciencedirect.com/science/article/pii/016...065T [2] Samson Abramsky, Achim Jung, Domain Theory, Pub. in: Handbook of Logic in Computer Science, Vol 3, Clarendon Press, Oxford, 1994 https://www.cs.bham.ac.uk/ ˜ axj/pub/papers/handy1.pdf [3] Samson Abramsky, C.-H. Luke Ong, Full abstraction in the lazy lambda calculus, Information and Computation, 105:159– 267, 1993 https://www.sciencedirect.com/science/article/pii/S08...0448 [4] H.P.Barendregt, The Lambda Calculus Its Syntax and Semantics, Studies in Logic and the foundations of mathematics, North-Holland, 1981 [5] Guy Blelloch, Robert Harper, λ-Calculus - The Other Turing Machine, Conference paper, Carnegie-Mellon University, July 2015 https://www.cs.cmu.edu/˜rwh/papers/lctotm/cs50.pdf [6] Luca Cardelli, Marcelo Fiore, Glynn Winskel (Ed), Computation, Meaning, and Logic: Articles dedicated to Gordon Plotkin, Electronic Notes in Theoretical Computer Science 172 (2007) https://www.sciencedirect.com/journal/electronic-...nce/vol/172 [7] Felice Cardone, J. Roger Hindley, History of Lambda-calculus and Combinatory Logic, Swansea University Mathematics Department Research Report No. MRRS-05-06, 2006 https://www.researchgate.net/publication/2283868...inatory_logic [8] B. Jack Copeland, The Church-Turing Thesis, The Stanford Encyclopedia of Philosophy (Summer 2020 Edition), Edward N. Zalta (ed.), https://plato.stanford.edu/archives/sum2020/entries/church-turing/ [9] O-J Dahl, E.W.Dijkstra, C.A.R.Hoare, Structured Programming, Academic Press, 1972 https://dl.acm.org/doi/pdf/10.5555/1243380 [10] B. A. Davey and H. A. Priestley, Introduction to Lattices and Order, Cambridge, 2002 (2nd Ed.) [11] Dina Goldin, Peter Wegner, The Church-Turing Thesis: Breaking the Myth, Lecture Notes in Computer Science 3526:152-168, June 2005 https://www.researchgate.net/publication/221652812_T...ing_the_Myth 27 FACS FACTS Issue 2021-2 July 2021 [12] J.A.Goguen, J.W.Thatcher, E.G.Wagner, E.B.Wright, Initial Algebra Semantics and Continuous Algebras, JACM, Vol 24, Issue 1, Jan. 1977 pp 68–95 [13] J. Roger Hindley, Jonathan Seldin, Introduction to Combinators and λ-Calculus, London Mathematical Society Student Texts 1, Cambridge, 1986 [14] Graham Hutton, Introduction to Domain Theory, 5 lectures, 1994 http://www.cs.nott.ac.uk/˜pszgmh/domains.html [15] Dexter Kozen, Church–Rosser Made Easy, Fundamenta Informaticae 105 1–8, DOI 10.3233/FI-2010-306 IOS Press, 2010 https://www.researchgate.net/publication/220444851_..._Made_Easy [16] Lukasz Lachowski, On the Complexity of the Standard Translation of Lambda Calculus into Combinatory Logic. REPORTS ON MATHEMATICAL LOGIC 53 (2018), 19–42 doi: 10.4467/20842589RM.18.002.8835 https://www.ejournals.eu/rml/2018/Number-53/art/12285/ [17] Kristen Nygaard and Ole-Johan Dahl The Development of the SIMULA Languages ACM SIGPLAN Notices. Vol. 13. No. 8. August 1978 https://phobos.ramapo.edu/˜ldant/datascope/simulahistory.pdf [18] David A. Schmidt, Denotational Semantics, Allyn and Bacon, 1986 https://people.cs.ksu.edu/˜schmidt/text/DenSem-full-book.pdf [19] Dana Scott, Outline of a Methematical Theory of Computation, (1977), Kiberneticheskij Sbornik. Novaya Seriya. 14. Also: PRG-02, Monograph, Oxford University Computing Laboratory, November 1970. https://www.cs.ox.ac.uk/files/3222/PRG02.pdf [20] Dana Scott, Christopher Strachey, Towards a Mathematical Semantics for Computer Languages, PRG-06, Monograph, Oxford University Computing Laboratory, August 1971, https://www.cs.ox.ac.uk/files/3228/PRG06.pdf [21] Dana Scott, Data Types as Lattices, SIAM J.